Pope Francis traveled to Rome's Basilica of St. Mary Major to pray that Mary protect and care for everyone attending World Youth Day in Brazil and for all young people around the world.
The pope spent more than 30 minutes in silent prayer in a side chapel before the basilica's famous Marian icon "Salus Populi Romani" (health of the Roman people).
The pope made the impromptu trip Saturday "to ask the Virgin for her protection for the upcoming apostolic journey to Brazil, for the young people who will gather for World Youth Day in Rio de Janeiro and for all young people in the world," said Jesuit Fr. Federico Lombardi, Vatican spokesman.
It was the same icon the pope turned to in prayer the day after he was elected pope in March and visited during the Marian month of May to pray the rosary.
"We know very well that he has a deep Marian devotion," Cardinal Santos Abril Castello, archpriest of the basilica, told Vatican Radio on Sunday.
Just as the pope prayed at the icon at the start of his pontificate to ask the Lord's protection of his papacy, the pope wanted to pray there for Mary's intercession for the large, important church event of World Youth Day, the cardinal said.
The pope laid a wreath of flowers near the icon and lit a candle that had on it this year's World Youth Day logo.
Abril said he told the pope the lit candle would be a sign of "the constant presence of a church in prayer, there in the temple of Our Lady, so as to protect the Holy Father and help him, and, most of all, so that his trip may reap all the fruits that he himself is hoping for."
The basilica was still open to the public and filled with visitors when the pope made his unannounced and unexpected visit. He spent another 30 minutes greeting people in front of the basilica's main altar asking them to accompany him on his July 22-29 trip "with prayers, with faith and with penance."
During his Angelus address Sunday in St. Peter's Square, Pope Francis again called for prayers for his trip.
Because of the large numbers of young people expected to participate during his weeklong visit, the pope said the event should be called World "Youth Week."
The pope said even those who will not be able to make the trip should be praying, listening and asking the same questions participants will be asking Jesus: "Lord, what must I do with my life? What is my path?"
He asked that people entrust these deep questions about life to Mary as he prayed for her intercession.
He said that Mary, who is "the mother of listening and service, teaches us to meditate within our heart on the word of her Son, to pray with fidelity and to always be more concretely attentive to the needs of our brothers and sisters."
He also thanked people in the crowd after seeing a large banner held aloft that said: "Have a good trip."
Pope Francis' first apostolic journey abroad will also have the prayers of his predecessor.
Pope Francis visited retired Pope Benedict XVI on Friday at the Vatican's Mater Ecclesiae Monastery -- where the retired pope lives -- to pray together and talk about the upcoming trip.
"Benedict XVI assured him of his prayers, recalling his intense and marvelous experiences at previous world gatherings with young people in Cologne, Sydney and Madrid," Lombardi said.
The pope also gave Pope Benedict a booklet with a detailed account of the trip itinerary, "so that he can spiritually participate in the events and, if he'd like to, follow the broadcasts," said the Vatican spokesman.
As soon as Pope Francis took off Monday in a chartered airplane from Rome to Rio, he tweeted from his @Pontifex account: "I am arriving in Brazil in a few hours and my heart is already full of joy because soon I will be with you to celebrate the 28th WYD."
He also tweeted to those who would like to be in Rio but can't, "May they feel at one with us in prayer."